1. Technical Field
The present disclosure relates generally to radio frequency (RF) integrated circuits, and more particularly, to RF power amplifiers with diode linearizers.
2. Related Art
Generally, wireless communications involve an RF carrier signal that is variously modulated to represent data, and the modulation, transmission, receipt, and demodulation of the signal conform to a set of standards for coordination of the same. Many different mobile communication technologies or air interfaces exist, including GSM (Global System for Mobile Communications), EDGE (Enhanced Data rates for GSM Evolution), and UMTS (Universal Mobile Telecommunications System) W-CDMA (Wideband Code Division Multiple Access). More recently, 4G (fourth generation) technologies such as LTE (Long Term Evolution), which is based on the earlier GSM and UMTS standards, are being deployed. Besides these mobile communications modalities, local area data networking modalities such as Wireless LAN (WLAN)/WiFi, WiMax, and so forth.
A fundamental component of any wireless communications system is the transceiver, that is, the combined transmitter and receiver circuitry. The transceiver encodes the data to a baseband signal and modulates it with an RF carrier signal. Upon receipt, the transceiver down-converts the RF signal, demodulates the baseband signal, and decodes the data represented by the baseband signal. An antenna connected to the transmitter converts the electrical signals to electromagnetic waves, and an antenna connected to the receiver converts the electromagnetic waves back to electrical signals.
The output of the transmitter is connected to a power amplifier, which amplifies the RF signals prior to transmission via the antenna. The receiver is connected to the output of a low noise amplifier, the input of which is connected to the antenna and receives inbound RF signals. A transmit/receive switch selectively interconnects the antenna to the output of the power amplifier during transmission, and to the input of the low noise amplifier during reception. Thus, the power amplifier, the low noise amplifier, and the antenna switch serves as key building blocks in RF transceiver circuitry. These components may be referred to as a front end circuit.
In most wireless communications such as the aforementioned WCDMA and 3G/4G cellular, it is important for the RF power amplifier to have high efficiency, as well as minimal distortion as characterized in terms of error vector magnitude (EVM), adjacent channel power ratio (ACPR) and so forth. Particularly in recent multiple-input multiple-output (MIMO) systems common in mobile devices, extremely low EVM is desirable so that dynamic long duration burst mode operation is possible. High efficiency RF power amplifiers such as class F, inverse class F, class E, and Doherty amplifiers, however, all exhibit non-linear performance because of lower gate bias voltages when implemented with complementary metal oxide semiconductor (CMOS) technology.
Accordingly, there is a need in the art for improved high efficiency, low distortion power RF power amplifiers. In particular, there is a need for linearizer networks to compensate for gain and phase deviation while maintaining high efficiency over a wide output power and frequency range.